Ok, so this is more of my process then an actual tutorial. But if you wondering how i've been doing all these things lately, this is pretty much how.
My process is championed by layering in Photoshop CS3. This allows for excessively easy editing of almost all, if not all elements of an image. This comes in handy, say if an Art Director said he wanted to see this guy in read. All i would need to so is just use the fill command on the color layer.
The tool i use primarily is the brush, and go between using pen pressure for opacity, and just using round, soft brush with no pen-pressure related changes. In all cases im using a rather low opacity for the bush. I work in black and white first, so i can focus on the light in space, and how it reacts to various surfaces. From there i go on to light color and so forth.
Another element that i did leave out of whats above is using 'noise'. Even though you can usually only tell at higher resolutions, all of my work recently has had a noise layer over it. Its important to say layer, and not just filter. I drop a 50% gray layer down in the middle of whatever im doing, set it to overlay, and add monochromatic noise. This breaks up the unnaturally smooth surfaces of photoshop drawn objects and adds another level of believability to the eye.
Texturing is always fun. It , like noise, helps to break up the computer panted surfaces to add another level believability. For a piece like this i have texture layers for burn marks, scratches, blood, rust, and others. Theres no (good) texture button in photoshop, everything i do is hand painted. Sometimes using layer effects can enhance the look of a texture painted on a layer. it pays to play around to see what you come up with.
Post effects are just stuff to make your design look pretty. Adding a ground, drop shadow, background, and other elements can be important. Though most of those are standard. Adding atmospheric elements can help, like depth of field, or distortion of colors depending on their distance from the camera. Even going back and adding small highlights on key areas to move your eye to focal points can help/ be important.
Hope this all gives some insight into what im doing. peace.